1. Field of Invention
The present invention relates to an image formation method applicable for electrophotographic apparatuses such as a copying apparatus, a printer, a facsimile and the like which use electrophotographic processes.
2. Description of Related Art
Conventionally, there have been many methods as an image formation method using the electrophotographic process and in a copying apparatus, a printer and the like, a method generally employed is a method comprising steps of forming an image on an electrophotographic photoreceptor by charging, exposing, and developing processes and transferring the obtained image to an object recording medium and fixing the image to obtain a copying image.
Recently, in the investigation and the development of the electrophotographic process and a material for the electrophotography, forming a link in the chain of tackling the environmental problems, technological developments have positively been achieved aiming to save energy, save resources and the like. Among the developments, for the purpose to save resources, investigations aiming to prolong lives of various members have positively been performed and also regarding a photoreceptor, it has highly been expected to further improve the durability of the photoreceptor.
As a photoreceptor, in place of a conventional inorganic photoreceptor, a variety of organic photoreceptors economical and excellent in the producibility and disposal property have practically been employed and in general, as one important factor to determine the life of an organic photoreceptor, there is wear of the surface layer. Regarding presently existing organic photoreceptors, so-called layered type ones comprising a charge transporting layer layered on a generating layer are the main stream and, in many cases, the charge transporting layer is to be the surface layer. However, regarding the charge transporting layers employed mainly today, although those with satisfactory functions in terms of the electric properties have been made available, a large quantity of compounds with low molecular weight compounds are dispersed in a binder resin and for that the original mechanical capabilities of the binder resin are deteriorated to result in a defect that the charge transporting layers have inevitably been weak in the wear.
Hence, a variety of proposals have been disclosed as the method for improving the mechanical strength of a charge transporting layer: 1) addition of a hard fine particle (Japanese Patent Application Laid-Open (JP-A) No. 6-282093); 2) addition of a substance for decreasing the surface energy such as silicone oil and the like; 3) modification of a binder resin (Idemitsu Technological Method, 36 (2), 88 (1993)) and the like; 4) formation of an overcoat layer on a charge transporting layer (e.g., JP-A No. 6-282092); 5) utilization of a charge transporting polymer compound (the specification of U.S. Pat. No. 4,801,517 and the like); and 6) curing of a charge transporting layer (JP-A No. 6-250423 and the like).
However, since the methods of the above-described 1) to 3) basically employ a binder resin in which low molecular weight compounds are dispersed, remarkable improvement in the mechanical strength cannot be expected. Further, the overcoat layer in the method of 4) contributes to decrease of the wear loss, yet it has a problem that an image is easily fogged especially under a high humidity since a conductive powder is dispersed in the binder resin. Meanwhile, in the case of the methods of 5) and 6), if a charge transporting polymer compound having sufficient capabilities is employed, the methods have an advantage that it is not necessary to disperse low molecular weight compounds, resulting in not only remarkable improvement of the mechanical properties but also applicability of conventional production facilities. Especially, in the method disclosed in the JP-A No. 6-250423, a charge transporting polymer compound is three-dimensionally bonded and therefore, further improved effect can be expected. However, in order to obtain such kind of charge transporting polymer compounds, at least one kind of monomers having reactive substituents is required to be synthesized and since the molecular design for improving the charge transporting property is greatly restricted, such a charge transporting polymer compound with sufficient capabilities has not been developed yet.
On the other hand, even in the case of employing a photoreceptor having a highly durable surface layer owing to an overcoating of, for example, a silicone type polymer, in some cases, the transferring efficiency is still deteriorated and a problem occurs in the images, and as a measure to solve such problems, a technique to use a toner in which resin particles are melted and bonded to one another in an aqueous medium is proposed (JP-A No. 2000-250259) and it has been tried to suppress fine powder generation, prevent decrease of the transferring efficiency, and improve the inferior cleaning property by making the toner shape even or making the toner surface irregular. However, no toner is available which does not contain or generate a fine powder at all and a photoreceptor is more or less polluted by adhesion of a fine powder.
Since many of the above-described adhering components are release agents with small molecular weights, there have been proposed methods: a method employing a release agent with a large molecular weight for a toner (JP-A No. 8-278653) and a method for scraping adhering components by a development method by bringing a carrier into contact with the photoreceptor (JP-A No. 9-304972). However, even these techniques cannot be said sufficient to achieve the original purposes without deteriorating other capabilities.